The present invention is related to a broad beam ion implantation system in which an ion beam is used to achieve a uniform ion implant.
A work piece, typically a wafer composed of, for example, semiconductor material, metal or a thin film on a substrate may be doped by irradiating the work piece with an ion beam. Ion beam implantation allows for tight control over the purity of the doped species, over the concentration of doping and over the depth of the doping. For an overview of ion beam implantation techniques, see for example, U.S. Pat. No. 4,578,589 for Apparatus and Methods For Ion Implantation issued to Derek Aitken and U.S. Pat. No. 4,733,091 for Systems and Methods for Ion Implantation of Semiconductor Wafers issued to Frederick Robinson et al.
In the prior art, generally, an ion beam with a relatively small radius is used for implantation. The ion beam systematically scans the two dimensional surface of the work piece. Alternately the location of the ion beam may be fixed and the work piece systematically moved through the ion beam until the two-dimensional surface of the work piece has been scanned.
The above-discussed method of ion beam scanning works best when the work piece has a fairly small surface area. However, when, for example, an ion beam with a fixed source is scanned across an eight inch wafer in order to dope the wafer uniformly, the substantial variation of the angle at which the ion beam strikes the wafer makes it very difficult to achieve uniform processing across the entire width of the wafer.
At least one technique has been attempted to achieve greater processing uniformity by producing an ion beam which, across the width of the work piece in a first direction, consistently strikes the work piece perpendicular to the surface. In order to perform a complete scan, the work piece is mechanically moved in a direction perpendicular to the first direction. See U.S. Pat. No. 4,367,411 for Unitary Electromagnet for Double Deflection Scanning of Charged Particle Beam issued to Peter Hanley et al. and see also D. W. Berrian, R. E. Kaim, J. W. Vanderpot and J. F. M. Westendorp, The ASM-220 Medium Current Implanter in Nuclear Instruments and Methods in Physics Research, B37/38 (1989), pp. 500-503.
Further, ion implantation systems have been built which mechanically move a wafer through an ion beam which is wider than the wafer. In the prior art, multi-aperture ion sources have been utilized and the technique has been used only for applications where doping uniformity requirements are not precise. See John P. Ruffel, D. H. Douglas-Hamilton and R. E. Kaim, A High Current, High Voltage Oxygen Ion Implanter in Nuclear Instruments and Methods in Physics Research, B21 (1987), pp. 229-234 and see D. H. Douglas Hamilton, John P. Ruffell and R. E. Kaim, End Station Design Wafer Quality Control for a High Current Oxygen Implanter, in Nuclear Instruments and Methods in Physics Research, B21 (1987), pp. 324-327.